Pressure to escalate is only going to get worse.

Colin H. Kahl is associate professor in the security studies program at Georgetown University’s Edmund A. Walsh School of Foreign Service and a strategic consultant at the Penn-Biden Center for Diplomacy and Global Engagement. From October 2014 to January 2017, he was Vice President Joe Biden's national security adviser.

What prompted the U.S. to act now, six years after the start of the civil war? The Washington Post's Amanda Erickson explains President Trump's decision to strike Syria. (Amanda Erickson,Jason Aldag/The Washington Post)

When Secretary of State Rex Tillerson travels to Moscow this week, topic No. 1 will be Syria — and the stakes could not be higher. If the Trump administration and the Kremlin are not able to come to a meeting of the minds on Syria, it could set the two nuclear powers on a dangerous collision course.

Early Friday morning in Syria, 59 U.S. Tomahawk missiles slammed into the Shayrat air base in retaliation for the unconscionable gassing of dozens of civilians by President Bashar al-Assad’s regime two days earlier. This was a stunning turnaround for President Trump, who urged his predecessor not to attack Syria under similar circumstances in 2013, and for an administration that had signaled indifference to Assad just five days before the attack.

Trump’s forceful action met with rave reviews across Washington and among U.S. allies. But the Russians — Assad’s chief patron — were furious. The Kremlin called the attack an “act of aggression,” and Prime Minister Dmitry Medvedev warned that the strikes put the United States and Russia “on the verge of a military clash.” Meanwhile, the Russian military suspended the hotline designed to avoid incidents between U.S. and Russian forces in Syria and announced its intentions to bolster Syrian air defenses.

However justified and morally satisfying, any use of military force is serious business, and even those limited strikes could lead the United States and Russia down an escalatory path.

The expansive way in which U.S. officials have talked about the purpose of the strikes increases the prospects of mission creep. In his statement announcing the attack, Trump framed it as essential to “prevent and deter the spread and use of chemical weapons.” Other administration officials justified the strikes on similar grounds. But Trump also described his decision as part of a broader effort to “end the slaughter and bloodshed in Syria,” suggesting that he may consider additional military action aimed at ending the Syrian war. The U.S. ambassador to the United Nations, Nikki Haley, made this explicit over the past few days, saying on Friday: “We are prepared to do more, but we hope that will not be necessary. It is time for all civilized nations to stop the horrors that are taking place in Syria and demand a political solution.”

The broader the administration’s goals in Syria, the more prone it will be to pressure to escalate there. Already, some regional allies that have long dreamed of dragging the United States into a war with Assad, such as Turkey, have described the strikes as “insufficient” and called for more forceful action. And congressional hawks, such as Sen. John McCain (R-Ariz.) and Sen. Marco Rubio (R-Fla.), are urging Trump to follow up on the strikes by providing Syrian opposition groups with more weapons, imposing a no-fly zone, and conducting further airstrikes to pressure Russia and Assad to agree to a political settlement. Meanwhile, the Syrian air force has already resumed bombing the northwestern town of Khan Sheikhoun — the same area the regime gassed last week. And as Assad continues to kill civilians, with or without chemical munitions, the calls for deeper U.S. involvement aimed at ousting Assad will mount.

If the United States goes down this road, the prospects of a military confrontation with Moscow are real. A few thousand Russian military personnel are distributed across Syria’s key military bases. Moscow has also placed some of the world’s most sophisticated air defense systems in Syria, and Russian planes police Syrian skies. So an extensive U.S. campaign aimed at coercing Assad by targeting Syrian air bases and command-and-control facilities would run big risks of killing Russian troops on the ground. The same holds for a no-fly zone, which would likely require targeting Syrian and Russian air defenses and could lead to air-to-air incidents between Russian and U.S. jets. Under any of these circumstances, the prospect of spiraling conflict is enhanced by Moscow’s decision to suspend the “deconfliction” channel between the Russian and U.S. militaries.

Compounding matters, in an effort to generate counter-leverage, Russia and the Assad regime are likely to respond to further U.S. strikes or a no-fly zone by reorienting their integrated air defense network toward U.S. and coalition aircraft engaged in fighting the Islamic State or by attacking opposition areas in northern Syria, where nearly 1,000 U.S. troops are on the ground. This could derail the counter-Islamic State campaign at the very moment when the militant group’s capital, Raqqa, is under assault by U.S.-backed forces. And it could put the lives of American service members in jeopardy.

There are also significant escalation risks even if the Trump administration doesn’t go down this path and sticks to the narrower stated objective of deterring further chemical attacks.

According to news reports, before the strikes, Trump was briefed on options to retaliate against Assad. One was to launch “saturation strikes” aimed at dozens of Syrian airfields and facilities, with the goal of destroying Assad’s ability to use his air force to carry out further chemical attacks. (This option was similar to the one reportedly contemplated by President Barack Obama in 2013.)

At the urging of Defense Secretary Jim Mattis and national security adviser H.R. McMaster, Trump rejected this option in favor of cruise missile strikes against a single air base. This option was reportedly viewed as proportional and much less likely to kill Russian soldiers. (Although around 100 Russian troops were reportedly stationed at Shayrat, the administration warned Moscow ahead of time, and the missiles struck the portion of the airfield away from Russian barracks.)

In other words, Trump chose a limited strike package precisely because he and his advisers understood the grave risks if the United States attacked a broader set of targets.

But therein lies a major dilemma for Trump moving forward. Successful deterrence requires a credible threat to hit Assad’s forces again if the regime continues to use chemical weapons or commits other transgressions. Yet Trump, having already rejected a larger military response out of apparent recognition of the dangers, may find it difficult to credibly signal he is willing to deploy this option in response to further actions by Assad down the line.

In this context, the danger of miscalculation is real. The Syrian dictator (perhaps prodded by Russia or Iran) may attempt to test Trump again, hoping to prove the president is a “paper tiger.” And Trump, having invested his personal credibility in standing firm, may find himself psychologically or politically compelled to respond, despite the very real risks that it could result in a direct military clash with Russia.

Before Tillerson arrives in Moscow for meetings on Wednesday, the administration needs a clear plan to avoid stepping on this slippery slope. It starts with Trump and his team being much more precise and consistent about what U.S. objectives are. Is the goal solely to deter more chemical attacks, or are they trying to end the Syrian conflict? If the latter, will the administration insist on Assad’s departure, or are they open to other possible formulas that de-escalate the war and defuse power away from Damascus but keep Assad in power?

On Sunday, administration officials seemed to suggest all of the above. Haley insisted on CNN, “There’s not any sort of option where a political solution is going to happen with Assad at the head of the regime.” Tillerson, however, warned against regime change during an ABC “This Week” interview, and told CBS’s “Face the Nation” that the Trump administration would seek to end Syria’s civil war through the creation of cease-fire zones and the resumption of a political process, saying Assad and Russia would have to participate in that solution.

Contributing to this uncertainty, Tillerson also said that the United States would not focus on initiatives to stabilize Syria until after the threat of the Islamic State has been “reduced or eliminated.”

Whatever the administration decides, their approach must blend credible military signaling with risk-mitigation steps (such as finding a way to reactivate the U.S.-Russia military channel). And the administration’s military actions must be backed by a diplomatic strategy that takes advantage of the leverage created by the strikes without overplaying Washington’s hand. Given Russia’s vital interests in Syria, Moscow is not likely to respond positively to U.S. ultimatums and maximalist positions. If the administration does not find a way to give the Kremlin a face-saving way out, conflict is much more likely than accommodation.

As the afterglow and applause of the missile strikes fade, finding a way to advance American interests in Syria while avoiding a war with Russia is the urgent task at hand. After all, sinking into a Syrian quagmire would be bad enough. World War III would be far worse.